Manufacturing method of hat-shaped steel sheet pile

Abstract

A method for manufacturing a hat-shaped steel sheet pile, wherein the rolled piece is subjected to rough rolling, intermediate rolling and finish rolling by hot rolling and then bent and formed, wherein the rolled piece includes a web corresponding portion, a flange corresponding portion, an arm corresponding portion and a joint corresponding portion, and a corner portion serving as a processing portion is formed at a connection portion between the web corresponding portion and the flange corresponding portion and a connection portion between the flange corresponding portion and the arm corresponding portion. In one or more intermediate rolling mills consisting of a single stand and a single hole type, the intermediate rolling is performed on the rolled piece in a hot state by using a hole type set on upper and lower hole type rollers at a height lower than a predetermined target product height and in multiple rolling passes, the bending and forming is performed in a hot state and is performed in a state where the temperature of the processing portion is above the phase transformation point, so that the rolled piece is formed into a predetermined target height and target width.

Description

Technical Field

[0001] (Cross-reference of related applications)

[0002] This application claims priority based on Japanese Patent Application No. 2020-041331 filed in Japan on March 10, 2020, and the contents of Japanese Patent Application No. 2020-041331 are hereby incorporated by reference.

[0003] The invention relates to a method for manufacturing a hat-shaped steel sheet pile. Background Art

[0004] As a method for manufacturing a hat-shaped steel sheet pile, a method of rolling a steel sheet pile into a product by hot rolling has become mainstream, and a method for manufacturing a hat-shaped steel sheet pile using a common groove rolling method is disclosed in Patent Documents 1 and 2. Hat-shaped steel sheet piles are manufactured by the manufacturing process disclosed in such known documents. Hereinafter, the prior art will be described based on these known documents with reference to the drawings.

[0005] The so-called groove rolling method is generally used to shape the hat-shaped steel sheet pile. Figure 1 This is a schematic diagram showing a conventional manufacturing process of a hat-shaped steel sheet pile. Figure 1 As shown, first, a rectangular piece, for example, is heated to a predetermined temperature using a heating furnace, and then a rough piece is manufactured using a rough rolling mill having a double pair of rolls forming a pass. Then, an intermediate piece is formed from the rough piece using an intermediate rolling mill having a double pair of rolls each forming a pass, and then a product having a joint portion is obtained using a finishing mill having a double pair of rolls forming a pass.

[0006] in addition, Figure 2 (a) to (f) are explanatory diagrams showing the forming process after the process performed by the rough rolling mill in the manufacture of the conventional hat-shaped steel sheet pile. Figure 2 (a) to (c) represent the process using a rough rolling mill. Figure 2 (d) and (e) represent the process using the intermediate rolling mill. Figure 2 (f) indicates a process using a finishing mill. Patent Document 1 mainly describes a method of rolling an intermediate piece, and Patent Document 2 describes a method of bending a joint portion of an intermediate piece to shape a joint portion of a product.

[0007] As the rectangular piece, a large billet or a slab is generally used. In the process of forming the rectangular piece into a rough piece, the rectangular piece is rolled sequentially using the configured pass in a rough rolling mill equipped with 2 to 3 pass types, thereby forming a rough piece. Then, in an intermediate rolling mill equipped with a total of 4 to 5 pass types, the rough piece is rolled sequentially using the configured pass types, thereby forming an intermediate piece. Here, as shown in FIG. Figure 2 The left joint and the right joint are asymmetrical (point symmetric) and have a large height difference. Figure 2 As shown in (e), the left arm and the right arm are tilted relative to the horizontal direction, so that the height of the left joint is aligned with the height of the right joint, and the main axis of inertia of the cross section is aligned with the pressing direction ( Figure 2 The vertical direction) is consistent, thereby suppressing the bending on the exit side of the rolling.

[0008] In addition, the joint part is bent and shaped around the base of the joint part to form the joint part. Figure 2 The product shown in (f) is as follows. Figure 1 and Figure 2 In the above-described conventional method for forming a hat-shaped steel sheet pile, when forming a product from a rectangular material, about 7 to 10 holes are used, and a total of about 30 processing steps are required.

[0009] In addition, the prior art disclosed in Patent Document 3 is also known: for the product formed by the above method, a roll forming device having a support roll, etc. (see Figure 3 ) is cold worked to produce hat-shaped steel sheet piles with cross-sectional shapes of different heights or widths.

[0010] Prior art literature

[0011] Patent Literature

[0012] Patent Document 1: Japanese Patent No. 4464865

[0013] Patent Document 2: Japanese Patent Application Publication No. 2007-237276

[0014] Patent Document 3: Japanese Patent Application Publication No. 2003-230916 Summary of the invention

[0015] Problem that the invention aims to solve

[0016] As can be seen from the above-mentioned Patent Documents 1 to 3, as a method for manufacturing a hat-shaped steel sheet pile, there is known a method for manufacturing a hat-shaped steel sheet pile. Figure 1 to Figure 3The process shown. Here, in the forming method of the prior art, in order to reduce the manufacturing cost, it is necessary to improve the manufacturing efficiency and the yield rate. In addition, as a means to improve the manufacturing efficiency and the yield rate, it is considered to reduce the number of hole types, for example. By reducing the number of hole types, the time loss caused by the handover of the rolled parts (rectangular parts, intermediate parts, etc.) between the hole types and the temperature drop of the rolled parts caused by the heat dissipation during this period can be suppressed. That is, the improvement of manufacturing efficiency can be sought, and then by suppressing the temperature drop of the rolled parts, the extension of the rolling elongation can be sought, and the removal ratio of the rolling defect parts at the front and rear ends of the rolled parts can be reduced, thereby improving the yield rate.

[0017] On the other hand, reducing the number of pass types means that the reduction of each pass type and the stretch at each pass type increase. However, since the strength of the double roll pair constituting the pass type is limited and the output of the rolling mill for driving the double roll pair is restricted, it is difficult to give a large reduction and stretch the rolled piece in a single pass (semi-reciprocating in the pass type). Therefore, it is necessary to use a pass type to perform multi-pass reversible rolling (hereinafter also referred to as pass type multi-pass rolling) with two or more passes to obtain the desired stretch (usually 1.8 or more).

[0018] Generally, steel sections such as hat-shaped steel sheet piles have a plate thickness distribution in the width direction. In order to roll such steel sections using the hole mold provided in the double roll pair, it is a basic principle to perform only a single pass rolling using each hole mold. In the past, except for the initial stage of rolling using a rough rolling mill (hereinafter referred to as rough rolling) and rolling using an intermediate rolling mill (hereinafter referred to as intermediate rolling), multi-pass rolling using the hole mold was not performed. The reason is that multi-pass rolling using the hole mold causes the metal (rolled workpiece) to not fill the hole mold (hereinafter referred to as wall thickness reduction), the metal to overflow from the hole mold (hereinafter referred to as burrs), and the rolled workpiece to bend. In the case of hat-shaped steel sheet piles, these become Fig. 20 The distortion shown in (a) Fig. 20 In addition, the reason why a certain degree of multi-pass rolling can be performed in the early stage of rough rolling and intermediate rolling is that the plate thickness of the rolled piece is relatively large, so the rigidity is high, and it is not easy to cause distortion, undulation, and bending. Even if wall thickness reduction and burrs occur, as long as they are relatively mild, they can be eliminated by subsequent rolling of the pass.

[0019] In a hat-shaped steel sheet pile, the flange is sandwiched on both sides by the web and the arm, and its elongation and widening are suppressed, so that no burrs are generated in the flange, but instead, compressive stress is easily generated. If the compressive stress exceeds the buckling limit stress, it buckles and generates undulations (hereinafter referred to as flange waves). On the contrary, when the wall thickness of the flange is reduced, the surface of the flange separates from the roller, and the roller cannot restrain the flange, causing distortion.

[0020] That is, when a hat-shaped steel sheet pile is rolled multiple times using multiple calibers (multi-pass rolling), there is a problem that the flange and web portions are not uniformly pressed down. Figure 4 As shown in FIG. 1 , the web of the hat-shaped steel sheet pile is horizontal and is repeatedly pressed down from the top and bottom in this state. Therefore, when the web and the flange are pressed down by the same amount in the roll gap direction, the actual stretching (tf+ΔF) / tf of the flange is smaller than the stretching (tw+ΔW) / tw of the web. Therefore, it is impossible to press the web and the flange with the same stretching during multiple passes while making the roll gap smaller in the same caliber. If multiple passes are performed reluctantly, rolling waves are generated or the length of the wire in the cross section varies greatly, making it difficult to perform stable rolling.

[0021] In addition, in particular, in the above-mentioned Patent Document 3, the rolling stand for hot rolling and the stand for cold working by roll forming are configured off-line, and the production of steel sheet piles as products is not performed continuously, so there is room for improvement in its production efficiency. Specifically, in the cold working by roll forming, the steel material temperature is low, so the springback during working becomes large, and it is necessary to give a large strain to the steel material in a cold state. In addition, if the temperature during working is low, there is a concern of degradation of the material such as reduced toughness. Fig.21 This is an explanatory diagram of the shape change of bending in cold working, and is a graph showing the change in the overall width of the raw material in the longitudinal direction after the raw material (steel material) without overall width change in the longitudinal direction is bent in a cold state as disclosed in Patent Document 3. Fig.21 As shown in the figure, in the bending forming in the cold state, the forming effect of the longitudinal end is smaller than that of the stable part, which easily leads to insufficient bending and widening of the overall width. Therefore, reprocessing and cutting may be required, which may cause the reduction of yield and productivity.

[0022] Therefore, in view of the above-mentioned problems, the object of the present invention is to provide a method for manufacturing steel sheet piles as follows: in intermediate rolling to finish rolling, a rolling mill having only one caliber is used to perform rolling at a height lower than the height of the desired steel sheet pile product, and then bending and forming are performed online to obtain a steel sheet pile product of the desired height. This method for manufacturing steel sheet piles can improve production efficiency, shorten rolling time and reduce costs.

[0023] Another object of the present invention is to provide a method for manufacturing a steel sheet pile that can prevent flange waves and twisting during rolling and stably perform multi-pass rolling of a groove shape in the intermediate rolling of manufacturing the steel sheet pile.

[0024] Solutions for solving problems

[0025] In order to solve the above-mentioned problems, according to the present invention, a method for manufacturing a hat-shaped steel sheet pile is provided, wherein the rolled part is subjected to rough rolling, intermediate rolling and finish rolling by hot rolling and then subjected to bending forming, and the method is characterized in that the rolled part includes a web corresponding part, a flange corresponding part, an arm corresponding part and a joint corresponding part, and a corner portion as a processing portion is formed at a connection portion between the web corresponding part and the flange corresponding part and a connection portion between the flange corresponding part and the arm corresponding part, and in one or more intermediate rolling mills composed of a single frame and a single hole type, the intermediate rolling is performed on the rolled part in a hot state at a height lower than a predetermined target product height and in multiple rolling passes using a hole type set on the upper and lower hole type rollers, and the bending forming is performed in a hot state and is performed in a state where the temperature of the processing part is above the phase transformation point, so that the rolled part is formed into a predetermined target height and a target width.

[0026] Effects of the Invention

[0027] According to the present invention, in the intermediate rolling to the finishing rolling, a rolling stand having only a single stand and a single caliber is used to perform rolling at a height lower than the desired height of the steel sheet pile product, and then bending and forming are performed online, thereby obtaining a steel sheet pile product of the desired height, thereby achieving improved production efficiency, shortened rolling time, and cost reduction. In addition, in the intermediate rolling of the steel sheet pile manufacturing, it is possible to prevent flange waves and twisting during rolling, and stably perform multi-pass rolling of the caliber. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic explanatory diagram showing a general manufacturing process of a hat-shaped steel sheet pile.

[0029] Figure 2 This is an explanatory diagram showing a forming process after a step performed by a rough rolling mill in the manufacture of a conventional hat-shaped steel sheet pile.

[0030] Figure 3 This is an explanatory diagram of a prior art for manufacturing a hat-shaped steel sheet pile having a cross-sectional shape with different heights or widths by cold working using a roll forming device.

[0031] Figure 4 It is an explanatory diagram regarding the correlation between the flange reduction amount ΔF and the web reduction amount ΔW in the hat-shaped steel sheet pile.

[0032] Figure 5 It is a schematic explanatory diagram of a rolling line according to an embodiment of the present invention.

[0033] Figure 6It is a schematic side sectional view of a bending machine.

[0034] Figure 7 This is a schematic front view of a bending machine.

[0035] Figure 8 It is an enlarged front view schematically showing the hole shape of the first frame.

[0036] Fig. 9 It is an enlarged front view schematically showing the hole shape of the second frame.

[0037] Fig.10 This is a graph showing the relationship between "roll gap - rolled material thickness" and "load" during bending.

[0038] Fig.11 This is a graph showing the relationship between "roll gap - rolled material thickness" and "web-flange angle" during bending.

[0039] Fig.12 This is a schematic diagram showing the dimensional relationship during bending.

[0040] Fig.13 This is an explanatory diagram regarding the change in shape of a rolled piece being bent in the first stand and the second stand. Fig.13 (a) shows a schematic cross-sectional view of the first frame before processing. Fig.13 (b) shows a schematic cross-sectional view of the first frame during processing. Fig.13 (c) is a schematic cross-sectional view showing the processing at the second frame.

[0041] Fig.14 This is an explanatory diagram regarding the contact portion of a finished workpiece in a bending machine.

[0042] Fig.15 This is an explanatory diagram regarding the contact points in a bending machine.

[0043] Fig.16 This is a schematic explanatory diagram of an example of the structure of a pass provided in the second intermediate rolling mill.

[0044] Fig.17 This is a schematic diagram for explaining other shapes of the pass used in the intermediate rolling.

[0045] Fig.18 This is a schematic diagram for explaining the case where the roll gap of the pass shape is changed.

[0046] Fig.19 This is an explanatory diagram related to Example 3.

[0047] Fig. 20This is an explanatory diagram showing a situation that occurs when the hole-type multi-pass rolling of the hat-shaped steel sheet pile is performed under inappropriate conditions. Fig. 20 (a) is an illustration of a distorted situation. Fig. 20 (b) is an explanatory diagram of the flange wave situation.

[0048] Fig.21 This is an explanatory diagram regarding the shape change of bending during cold working.

[0049] Fig. 22 It is an explanatory diagram regarding the contact state with the grooved roller. DETAILED DESCRIPTION

[0050] The following is an explanation of the embodiments of the present invention with reference to the accompanying drawings. In addition, in this specification and the accompanying drawings, the same reference numerals are given to components having substantially the same functional structure, thereby omitting repeated explanations. In addition, in this embodiment, a case where a hat-shaped steel sheet pile is manufactured as a steel sheet pile product is explained.

[0051] (Rolling line configuration)

[0052] Figure 5 This is an explanatory diagram of a rolling line L (single-dot chain line in the figure) for manufacturing a hat-shaped steel sheet pile according to an embodiment of the present invention and a rolling mill equipped in the rolling line L. Figure 5 In the figure, the rolling direction of the rolling line L is indicated by the arrow, and the rolled material flows in this direction, and is rolled and bent in each rolling mill and bending machine on the production line to form a product. Figure 5 In the figure, a rolling method in which the rolled material is reciprocated multiple times in the same rolling mill (so-called multi-pass rolling) is also described with a single-dot chain line.

[0053] like Figure 5 As shown, a roughing mill 10, a first intermediate mill 13, a second intermediate mill 16, a finishing mill 19, and a bending machine 20 are sequentially arranged from the upstream on the rolling production line L. In addition, an edge rolling mill 14 is arranged adjacent to the first intermediate mill 13 on the upstream side of the first intermediate mill 13, and an edge rolling mill 17 is arranged adjacent to the second intermediate mill 16 on the downstream side of the second intermediate mill 16.

[0054] In the rolling line L, the rectangular piece (rolled piece) heated in a heating furnace (not shown) is sequentially hot-rolled in the rough rolling mill 10 to the finishing rolling mill 19, and then hot-formed by the bending forming machine 20 to become a final product. In addition, for the sake of explanation below, the rolled piece rolled by the rough rolling mill 10 is also referred to as a rough piece, the rolled piece rolled by the first intermediate rolling mill 13 to the second intermediate rolling mill 16 is also referred to as an intermediate piece, and the rolled piece rolled by the finishing rolling mill 19 is also referred to as a finished piece 19a. That is, the product formed by forming (changing the cross section) the finished piece 19a by the bending forming machine 20 becomes the final product (i.e., a hat-shaped steel sheet pile product).

[0055] Here, the rough rolling mill 10, the first intermediate rolling mill 13, the second intermediate rolling mill 16, the finishing rolling mill 19, and the accompanying edge rolling mills 14 and 17 arranged in the rolling production line L are common equipment used in the manufacture of steel sheet piles in the past, so the description of their detailed device structure, etc. is omitted in this embodiment.

[0056] (Structure of bending machine)

[0057] Next, the detailed structure of the bending machine 20 will be described with reference to the drawings. Figure 6 is a schematic side sectional view of the bending machine 20, Figure 7 It is a schematic front view of the bending machine 20. Figure 6 , Figure 7 The bending machine 20 shown in the figure is used to bend (bend) the finished workpiece 19a after the finish rolling in the finishing mill 19. Figure 7 2 is a schematic front view of a first frame 22 of a bending machine 20 described below. Here, in the present embodiment, the bending machine 20 is described as being composed of two forming frames (forming frames 22 and 23 described below), but the bending machine 20 may also be composed of a single frame or any plurality of frames.

[0058] like Figure 6 As shown, the bending machine 20 of this embodiment includes two forming frames 22 and 23 (hereinafter also referred to as the first frame 22 on the upstream side and the second frame 23 on the downstream side) arranged adjacent to each other in series. Figure 7 As shown, each frame 22, 23 is respectively provided with a forming hole (hole 45, 55 described later) composed of an upper hole roller and a lower hole roller, and the hole shape becomes different in the first frame 22 and the second frame 23.

[0059] Here, the roller structures and hole shapes of the first frame 22 and the second frame 23 are described. Figure 8 2 is an enlarged front view schematically showing the hole shape of the first frame 22. Fig. 92 is an enlarged front view showing a schematic hole shape of the second frame 23. Figure 8 The cross-sectional shape of the finished product 19a before being formed by the bending forming machine 20 is shown by a single-dot chain line. Fig. 9 The cross-sectional shape of the finished product 19a' before being formed in the second frame 23 is illustrated by a single-dot chain line. In addition, the following describes the case where a substantially hat-shaped rolled product is bent in an open position (where the web corresponding portion described later is located at the bottom and the arm corresponding portion is located at the top).

[0060] like Figure 7 and Figure 8 As shown, an upper hole-shaped roller 40 and a lower hole-shaped roller 41 are provided in the first frame 22 in a manner supported by a housing 44, and a hole-shaped roller 45 is formed by the upper hole-shaped roller 40 and the lower hole-shaped roller 41. The shape of the hole-shaped roller 45 from the portion corresponding to the flange to the portion corresponding to the joint portion becomes the shape immediately before becoming a hat-shaped steel sheet pile product (i.e., a substantially hat-shaped steel sheet pile product shape). The hole-shaped roller 45 is used to change the angle formed by the portion corresponding to the flange of the finished workpiece 19a (i.e., the flange corresponding portion) and the portion corresponding to the web of the finished workpiece 19a (i.e., the web corresponding portion), and the angle formed by the above-mentioned flange corresponding portion and the portion corresponding to the arm of the finished workpiece 19a (i.e., the arm corresponding portion), respectively, so as to bend the height and width of the finished workpiece 19a into a predetermined shape (i.e., a cross-sectional shape similar to the product). In particular, when manufacturing a hat-shaped steel sheet pile, the following method is adopted: the rolled product (rough product to finished product 19a) is rolled in a shape with a low height in the rough rolling mill 10 to the finishing rolling mill 19, and the rolled product is bent in a bending machine 20 in a manner to increase the height of the rolled product to the desired product height. In this way, a large-sized hat-shaped steel sheet pile product can be manufactured.

[0061] In addition, if Fig. 9 As shown, an upper hole-shaped roller 50 and a lower hole-shaped roller 51 are provided in the second frame 23 in a manner supported by a housing 54, and a hole-shaped roller 55 is formed by the upper hole-shaped roller 50 and the lower hole-shaped roller 51. The hole-shaped roller 55 is formed into a shape close to the desired product shape, and is used to change the angle formed by the portion corresponding to the flange (i.e., the flange corresponding portion) and the portion corresponding to the web of the finished workpiece 19a (i.e., the web corresponding portion) formed by the first frame 22 of the bending machine 20, and the angle formed by the above-mentioned flange corresponding portion and the portion corresponding to the arm (i.e., the arm corresponding portion), respectively, so as to form the flange shape, the arm shape, and the joint shape into a predetermined shape (i.e., the shape of the product). That is, in the second frame 23, the inclination angle of the flange corresponding portion, which is insufficient with respect to the product shape during the forming in the first frame 22, is deformed to an angle corresponding to the product shape.

[0062] (Roll gap during bending)

[0063] Here, the roll gaps (roll gaps between the upper groove roll 40 and the lower groove roll 41 and the roll gaps between the upper groove roll 50 and the lower groove roll 51) in the above-mentioned grooves 45 and 55 during bending are configured to be larger than the thickness of the flange corresponding portion and the web corresponding portion of the finished workpiece 19a. That is, in the bending machine 20, the plate thickness of the finished workpiece 19a is not reduced, and the groove rolls of the first frame 22 and the second frame 23 and the finished workpiece 19a are configured to be bent only at a part of the predetermined portions described later.

[0064] In addition, as described later, during bending, the grooved rollers of the first frame 22 and the second frame 23 and the finished workpiece 19a may be pressed down in addition to being in contact at a predetermined portion. "Contact" in this specification refers to a state in which only one of the upper surface and the lower surface of a specific portion of the finished workpiece 19a abuts against the circumferential surface of the grooved roller in the bending machine 20. In contrast, "pressing down" refers to a state in which both the upper surface and the lower surface of a specific portion of the finished workpiece 19a abut against the grooved roller in the bending machine 20 and a force is applied thereto in order to reduce the thickness.

[0065] For example, it is preferable that the roll gap at the portion corresponding to the web corresponding portion and the flange corresponding portion is larger than the thickness of the flange corresponding portion and the web corresponding portion of the finished workpiece 19a by about 0.5 mm to 3 mm. In addition, the roll gap at the portion of the hole 45 and the hole 55 related to the arm corresponding portion of the finished workpiece 19a may be configured to be larger than the thickness of the arm corresponding portion in the entire cross-sectional area. When the allowable range of the roll gap is smaller than 0.5 mm, there is a possibility that the thickness is reduced and the load of the bending machine 20 is increased due to the change in the plate thickness of the finished workpiece 19a. When the allowable range of the roll gap is larger than 3 mm, there is a possibility that the inclination angle of the flange corresponding portion cannot be formed to the target angle.

[0066] Here, the inventors of the present application have conducted more detailed studies on the allowable range of the roll gap at the portions facing the web corresponding portion and the flange corresponding portion, the forming machine load characteristics (changes in load and torque), and the formability (accuracy of the bending angle). Fig.10 It is a graph showing the relationship between "roll gap - material thickness (i.e., the allowable value of the roll gap)" and "load and torque" applied to the bending machine 20 when the finished workpiece 19a is bent. Fig.11 It is a graph showing the relationship between "roll gap - material thickness (ie, the allowable value of the roll gap)" during the bending of the finished product 19a and the "angle between the web and flange" after the bending.

[0067] also, Fig.10 , Fig.11 The diagram shows that a finished product 19a having a roughly hat-shaped steel sheet pile shape with dimensions of 1400 mm in width, 14.7 mm in web thickness, 11.4 mm in flange thickness, and 40° in flange angle (140° between web and flange) is bent using the first frame 22 with a flange angle of 56° (124° between web and flange). Fig.12 2 is a schematic diagram showing the dimensional relationship during bending forming at the first frame 22. Fig.12 The differences between the roll gaps T1, T2, T3 at the corresponding parts of the web, flange and arm and the thicknesses t1, t2, t3 of the finished workpiece 19a at each part, i.e., the values ​​of "T1-t1", "T2-t2", "T3-t3", were set as the allowable values ​​of the roll gap and a study was conducted.

[0068] like Fig.10 As shown in the figure, when the allowable value of the roll gap is 0.5 mm or more during bending, the load and torque change gently, but when the allowable value of the roll gap is less than 0.5 mm, especially less than 0.2 mm, the increase rate of the load and torque increases, and the increase is significant when the value is less than 0 mm (i.e., the thickness decreases). Based on this result, it can be seen that in order to suppress the forming load (load and torque) of the bending machine 20 to a low level, considering the actual thickness change, it is preferable to set the allowable value of the roll gap to be 0.5 mm or more.

[0069] In addition, if Fig.11 As shown in FIG. 1 , as long as the allowable value of the roll gap during bending is 0.5 mm to 3 mm, bending can be performed roughly at the desired target angle (i.e., about 124°±1° of the target web-flange angle). However, when the allowable value of the roll gap exceeds 3 mm, there is a tendency that the pressing by the grooved roll is reduced, the bending becomes weak, and the web-flange angle becomes larger than the target value. Therefore, there is a case where the flange angle needs to be corrected to a large extent in the finishing process after bending. That is, especially in the final stand, the upper limit of the allowable value of the roll gap is preferably set to 3 mm.

[0070] (Shape change during bending)

[0071] Next, the forming of the rolled material in the above-mentioned stands 22 and 23 will be described. Fig.13 1 is an explanatory diagram of the shape change of the rolled product (finished product 19a) being bent in the first stand 22 and the second stand 23. Fig.13 (a) shows a schematic cross-sectional view of the first frame 22 before processing. Fig.13 (b) shows a schematic cross-sectional view of the first frame 22 during processing. Fig.13(c) shows a schematic cross-sectional view of the second frame 23 during processing. Fig.13 As shown in (a), the finished product 19a is a substantially hat-shaped product, and includes: a substantially horizontal web corresponding portion 60; flange corresponding portions 62, 63, which are connected to both ends of the web corresponding portion 60 by means of corner portions 70 having a predetermined angle (indicated as angle α in the figure) larger than the angle of the product shape; arm corresponding portions 65, 66, which are connected to the ends of the flange corresponding portions 62, 63 on the sides different from the connection side to the web corresponding portion by means of corner portions 71; and joint corresponding portions 68, 69, which are formed at the top ends of the arm corresponding portions 65, 66. In addition, the finished product 19a is made to have a thickness substantially equal to the thickness of the product by rolling in the finishing mill 19, and the shapes of the joint corresponding portions 68, 69 are also substantially equal to the joint shape of the product.

[0072] Here, the dimensions may be designed so that the thickness of the corner portion 70 (hereinafter also referred to as the web-flange corner portion 70) is thicker than the thickness of the product plate. The thickness of the web-flange corner portion 70 can be determined by the thickness of the product plate in the roughing mill 10, the first intermediate mill 13, the second intermediate mill 16, the finishing mill 19, etc. (see Figure 1 ) and rolled to the desired plate thickness according to the rolling conditions and rolling design during hot rolling performed in the process.

[0073] Similarly, the dimensions may be designed so that the thickness of the corner portion 71 (hereinafter also referred to as the flange-arm corner portion 71) is thicker than the product plate thickness. The thickness of the flange-arm corner portion 71 can be determined by the thickness of the rough rolling mill 10, the first intermediate rolling mill 13, the second intermediate rolling mill 16, the finishing rolling mill 19, etc. (see Figure 1 ) and rolled to the desired plate thickness according to the rolling conditions and rolling design during hot rolling performed in the process.

[0074] Should Fig.13 The finished product 19a shown in (a) is formed in the hole 45 of the first frame 22 by reducing the angle α between the web corresponding portion 60 and the flange corresponding portions 62, 63 (becoming Fig.13 The angle α shown in (b) 1 ) bending forming method, such as Fig.13 As shown in (b), the height is close to the desired product height. That is, the first frame 22 performs bending processing to increase the height of the finished product 19a.

[0075] Next, if Fig.13 As shown in (c) of FIG. 2 , the finished product 19 a is bent into a substantially product shape in the hole 55 of the second frame 23 .

[0076] (Contact area during bending)

[0077] in addition, Fig.141 is an explanatory diagram of the contact portion of the finished workpiece 19a in the bending machine 20. Fig.14 (a) to (d) of FIG. 1 each represent an example of a contact portion. Fig.14 In the hole type 45 of the first frame 22 and the hole type 55 of the second frame 23, each hole type roller contacts the finishing workpiece 19a only at a predetermined portion, and the plate thickness is not reduced. For example, Fig.14 As shown in (a), the specific contact parts between the grooved roller and the finished workpiece 19a are the inner sides 70a and 70b of the corners between the web corresponding part 60 and the flange corresponding parts 62 and 63 and the inner sides 71a and 71b of the corners between the flange corresponding parts 62 and 63 and the arm corresponding parts 65 and 66. Here, "contact" means that at least the material is in contact with the grooved roller, and a force pressing the material may also be applied.

[0078] like Fig.14 As described in (a) of FIG. 1 , the contact parts 70a and 70b are located inside the corner 70 that is the boundary between the web corresponding part 60 and the flange corresponding parts 62 and 63. On the other hand, the contact parts 71a and 71b are located inside the corner 71 that is the boundary between the flange corresponding parts 62 and 63 and the arm corresponding parts 65 and 66. At the contact parts 71a and 71b, reaction forces are generated in directions that are balanced with the reaction forces at 70a and 70b, respectively.

[0079] Here, Fig.14 The lower surface (outer surface) center portion 60a of the web corresponding portion 60 shown in (b) is in contact with the grooved roller facing the lower surface (outer surface) center portion 60a of the web corresponding portion 60, so that the angle formed by the flange corresponding portions 62, 63 and the web corresponding portion 60 can be efficiently bent. The reason is that during bending, the web corresponding portion 60 is warped in the downward direction in the figure, so by making the lower grooved roller contact with the lower surface center portion 60a separated from the two sides (corner portion 70) of the web corresponding portion 60, a bending moment can be effectively applied to both ends of the web corresponding portion 60.

[0080] In addition, in order to make the arm corresponding parts 65 and 66 substantially horizontal, the upper surfaces (outer surfaces) 65a and 66a of the arm corresponding parts 65 and 66 are the contact parts at least in the second frame 23 as the final frame. Fig.14 As shown in (c), in the hole 45 of the first frame 22 and the hole 55 of the second frame 23, the inner upper parts 62a, 63a of the flange corresponding parts 62, 63 of the finished workpiece 19a are brought into contact with the upper hole rollers 40, 50, and the outer lower parts 62b, 63b of the flange corresponding parts 62, 63 are brought into contact with the lower hole rollers 41, 51. Fig.14 The contact at the position shown in (c) can cause the corners 70 and 71 to be bent at three points based on the shape of the hole-shaped rollers, thereby performing high-precision bending forming.

[0081] In addition, you can also Fig.14 As shown in (d), in addition to making Fig.14 In addition to the parts described in (a) to (c) of FIG. 1 , the upper surfaces (outer surfaces) 68a and 69a of the bonding portion corresponding parts 68 and 69 are also brought into contact with the upper hole-shaped rollers 40 and 50. Fig.14 By contacting the parts shown in (d), the corresponding parts 68 and 69 of the joint can be formed to be roughly horizontal, thereby performing bending forming with higher accuracy.

[0082] Here, refer to Fig. 22 Further details Fig.14 (d) shows the contact state between the finished workpiece 19a and the hole-shaped roller during bending. Fig. 22 The dotted line encloses the hole-shaped roller and Fig.14 The contact portion corresponding to the contact position of the finishing workpiece 19a of (d) is indicated. The corners 90 (90a to 90d) opposite to the corners of the boundary between the web corresponding part 60 and the flange corresponding parts 62, 63 of the finishing workpiece 19a of the upper and lower hole-shaped rollers, and the corners 94 (94a to 94d) opposite to the corners of the boundary between the flange corresponding parts 62, 63 and the arm corresponding parts 65, 66 of the upper and lower hole-shaped rollers are usually formed with rounded corners (curvature portions). The corners 90a and 90c opposite to the inner sides 70a and 70b of the corners of the boundary between the web corresponding part 60 and the flange corresponding parts 62, 63 of the finishing workpiece 19a of the upper hole-shaped roller 40 (or 50) are made to contact the inner sides 70a and 70b of the corners. At this time, the outer side of the corner portion of the boundary between the web corresponding portion 60 and the flange corresponding portions 62, 63 does not contact the corner portions 90b, 90d of the lower hole-shaped roller 41 (or 51) that are opposite to the outer side of the corner portion of the boundary. The lower hole-shaped roller 41 (or 51) contacts the portion that is opposite to the central portion 60a of the lower surface (outer side) of the web corresponding portion 60 of the finished workpiece 19a and the portion that is opposite to the outer lower portions 62b, 63b of the flange corresponding portions 62, 63.

[0083] In addition, the corners 94b and 94d of the lower hole-shaped roller 41 (or 51) that are opposite to the inner sides 71a and 71b of the corners of the boundary between the flange corresponding parts 62 and 63 and the arm corresponding parts 65 and 66 of the finished workpiece 19a are brought into contact with the inner sides 71a and 71b of the corners of the boundary. At this time, the outer sides of the corners of the boundary between the flange corresponding parts 62 and 63 and the arm corresponding parts 65 and 66 are not brought into contact with the corners 94a and 94c of the upper hole-shaped roller 40 (or 50) that are opposite to the outer sides of the corners of the boundary. The upper hole-shaped roller is brought into contact with the portions that are opposite to the upper surfaces (outer surfaces) 65a and 66a of the arm corresponding parts 65 and 66 of the finished workpiece 19a and the portions that are opposite to the inner upper parts 62a and 63a of the flange corresponding parts 62 and 63. In addition, the upper surfaces (outer surfaces) 68a and 69a of the joint corresponding parts 68 and 69 are in contact with the portions of the upper hole-shaped rollers 40 and 50 that are opposite to the upper surfaces (outer surfaces) 68a and 69a. Fig.14 (d) is the contact state with the upper and lower hole-shaped rollers, but for Fig.14 The same is true for (a) to (c) above. Similarly, the grooved roller facing the contact portion of the finishing material 19a may be brought into contact with the contact portion of the finishing material 19a.

[0084] In addition, refer to Fig.14 (a) to (d) of FIG. 1 have described preferred contact positions with respect to the finished workpiece 19a during bending forming, but as Fig.14 and Fig. 22 As shown, the positions to be contacted during bending forming are not in a position structure to press down the plate thickness of the finished workpiece 19a. Specifically, the structure is not to press (i.e., press down) a specific portion of the finished workpiece 19a from both sides by both upper and lower grooved rollers, and the gap between the upper and lower grooved rollers is also configured to be larger than the plate thickness of the finished workpiece 19a, so that the plate thickness is not pressed down. If the web corresponding portion 60 and the flange corresponding portions 62 and 63 are not pressed down, there is no need to increase the pressing reaction force unnecessarily.

[0085] In addition, although Fig.14 and Fig. 22 In the embodiment of the present invention, a part of each hole-shaped roller is in contact with each corner 70, 71, but the contact part of each hole-shaped roller in the present invention is not limited to this. Fig.14 and Fig. 22 In addition to the contact points described, further contact points are provided.

[0086] Fig.15 1 is an explanatory diagram of the contact portion of the finished workpiece 19a in the bending machine 20. Fig.15 (a) to (d) show other examples of contact locations. Fig.14The same contact parts are marked with the same reference numerals, and their descriptions are omitted. Fig.15 As shown, it can also be, as a contact part, in addition to Fig.14 In addition to the contact parts shown, there are also outer sides 70c, 70d of the corner portion 70 that is the boundary between the web corresponding portion 60 and the flange corresponding portions 62, 63 (hereinafter also referred to as the outer sides 70c, 70d of the web-flange corner portion) and outer sides 71c, 71d of the corner portion 71 that is the boundary between the flange corresponding portions 62, 63 and the arm corresponding portions 65, 66 (hereinafter also referred to as the outer sides 71c, 71d of the flange-arm corner portion).

[0087] That is, the contact portion between each grooved roller and the finishing material 19a is set to Fig.15 In the case of the portion shown, the web-flange corner portion 70 and the flange-arm corner portion 71 of the finished product 19a are in contact with both the upper and lower grooved rolls and are pressed down from both sides.

[0088] As described above, in the hot rolling (rough rolling, intermediate rolling, finishing rolling, etc.) as the upstream process of the bending forming, after rolling in such a manner that the plate thickness of the web-flange corner 70 and the flange-arm corner 71 is thicker than the product plate thickness, the material may be conveyed to the bending forming machine 20. In addition, the roll gap between the upper and lower grooved rollers at the portion facing the web-flange corner 70 and the flange-arm corner 71 of the finished workpiece 19a may be set so as to achieve the product plate thickness. When such a dimensional structure is achieved, the web-flange corner 70 and the flange-arm corner 71 of the finished workpiece 19a, which are thicker than the product plate thickness, are pressed down by both the upper and lower grooved rollers in the bending forming machine 20, and the material of the finished workpiece 19a is bent as a whole.

[0089] Thus, although in principle no pressing is performed during the bending of the finished product 19a, it is also possible to press only a predetermined portion (see Fig.15 ) is pressed down. If the finished product 19a is pressed down, the area being pressed down undergoes plastic deformation in the plate thickness direction as a whole. Due to the plastic deformation caused by pressing down, the stress distribution in the plate thickness caused by bending moves toward the compression side as a whole, and the bending moment acting on the corner is reduced. Therefore, within the range where plastic deformation occurs in the plate thickness direction as a whole, the springback after bending becomes very small.

[0090] That is, Fig.15As shown, if the web-flange corner 70 and the flange-arm corner 71 are pressed down while the bending is performed, compared with the case where the web-flange corner 70 and the flange-arm corner 71 are not pressed down, although the forming load increases, the increase in the compressive stress on the inner side of the thickness direction of the corners 70 and 71 of the finished workpiece 19a during the bending can be suppressed, and the tensile stress on the outer side can be reduced, so that the rebound after forming can be reduced, thereby reducing the change in the dimensional shape of the finished workpiece 19a in the length direction. As a result, rolling can be performed in the best shape without being restricted by the shape (angle) of the product, thereby improving productivity and yield. In addition, large-section products with excellent dimensional accuracy can be manufactured at low cost without being restricted by the roller diameter of the rolling mill. Furthermore, compared with the case of cold working, the equipment can be made smaller, and the dimensional shape and material can be stabilized.

[0091] In addition, Fig.15 In the bending forming of the structure shown, if the reduction rate of the web-flange corner 70 and the flange-arm corner 71 exceeds 20%, the tensile balance of each part in the cross section cannot be achieved, and the shape may be distorted. Therefore, the reduction rate in bending forming is preferably less than 20%, and more preferably 2% to 10%. As long as it is reduced by 2%, the web-flange corner 70 and the flange-arm corner 71 as a whole in the plate thickness direction become a plastic area, which can reduce the springback after bending forming. However, in order to meet such a reduction rate condition, it is necessary to pre-adjust the plate thickness of the web-flange corner 70 and the flange-arm corner 71 of the rolled piece in the rolling process.

[0092] In addition, when the bending machine 20 is composed of multiple frames, all the frames can also be used to press down the corners 70 and 71, but as long as the corners 70 and 71 are pressed down in at least the final frame (the second frame 23 in this embodiment), the effect of reducing the springback after forming can be achieved.

[0093] (Effect)

[0094] According to the above reference Fig.14 , Fig.15 The structure described above is a structure in which the roll gap between the upper and lower hole-shaped rollers of the bending and forming machine 20 is larger than the thickness of the flange corresponding part and the web corresponding part of the finished workpiece 19a. Even when there is a difference in the thickness of the left and right flange corresponding parts of the rolled workpiece due to the axial deviation of the upper and lower hole-shaped rollers during, for example, a rolling process (rough rolling to finishing rolling), it is possible to avoid a situation in which only the flange corresponding part on one side is bent while the thickness is reduced, thereby making the material flow unstable.

[0095] Furthermore, the bending forming is performed in a hot state as described above. Preferably, the finishing mill 19 and the bending forming machine 20 are arranged in series, and the finishing rolling and bending forming are continuously performed in a hot state, so as to reduce the temperature drop of the rolled piece. Here, the finishing rolling and bending forming in a hot state refer to rolling and forming at a temperature before the phase transformation of the rolled piece is completed. By performing bending forming under such conditions, compared with the conventional bending forming performed in a cold state, the forming load applied to the bending forming machine 20, the elongation and toughness reduction caused by the bending forming, and the material degradation and residual stress can be reduced.

[0096] In this way, Fig.13 In the bending machine 20, the finished product 19a is formed by the hole-shaped rollers, and the hole-shaped roller shape generates a three-point bending moment at the corner, so that the corner is further bent to approach the product shape. Fig.14 or Fig.15 In addition, although the reference Fig.13 (b) and Fig.13 (c) illustrates the forming performed in each hole type 45, 55, but these bending operations are performed continuously on a piece of material (finished workpiece 19a), and usually a piece of material is formed in a state where it passes through both the first frame 22 and the second frame 23 at the same time (i.e., in a serial state).

[0097] In the manufacturing method of the steel sheet pile of the present embodiment, a structure is set to bend and form using the bending forming machine 20 constructed as described above, and it is possible to efficiently manufacture a hat-shaped steel sheet pile product without using a large and complicated rolling mill or a large number of rolling mills. In addition, it can also be applied to the case of manufacturing a large hat-shaped steel sheet pile product without any problem.

[0098] In addition, in this embodiment, the bending forming is performed in a hot state by connecting the bending forming machine 20 directly after the finishing mill 19. As a result, the temperature of the rolled material entering the bending forming machine 20 can be maintained high, so there is no need to reheat the rolled material during bending forming, and rolling and bending forming can be performed continuously. According to the bending forming in a hot state, the bending reaction force is smaller, the springback is smaller, and the number of bending stages is smaller than that in a cold state.

[0099] An example of an embodiment of the present invention is described above, but the present invention is not limited to the illustrated embodiment. It is obvious that various variations or modifications can be thought of within the scope of the ideas described in the claims, and it is understood that these also belong to the protection scope of the present invention.

[0100] (Shape of the hole used in the intermediate rolling)

[0101] For example, in the above-mentioned embodiment, the bending process in the bending forming machine 20 is described, but when manufacturing the hat-shaped steel sheet pile, there is room for improvement in the pass shape and the like of the rolling mill other than the bending forming machine 20. The preferred shape of the pass used for the intermediate rolling is described below.

[0102] According to the research of the inventors of the present application, in the intermediate rolling process, even when rolling is performed while maintaining the balance between the elongation of the web corresponding portion 60 and the elongation of the flange corresponding portions 62 and 63, the upper and lower roller diameters of the upper and lower grooved rollers differ according to the location, so the relative sliding speed between the rolled product (particularly the flange corresponding portions 62 and 63) and the rollers differs according to the location. In the flange corresponding portions 62 and 63, at the location where the difference between the upper and lower roller diameters is large, the elongation of the rolled product is suppressed by the difference in the circumferential speed of the upper and lower rollers, while at the location corresponding to the pitch line (hereinafter referred to as the "neutral line") where the diameters of the upper and lower rollers are equal, elongation is likely to occur, so that compressive stress is likely to be generated in the flange near the neutral line at the roll gap exit in the longitudinal direction, and when the compressive stress exceeds the buckling limit, a shape defect called a so-called flange wave is generated in the flange corresponding portions 62 and 63.

[0103] In particular, when manufacturing a large steel sheet pile such as a hat-shaped steel sheet pile having a large flange width / flange thickness ratio, the elongation of the flange near the neutral line tends to become relatively large relative to the elongation of the web, and the compressive stress in the longitudinal direction acts from the roll gap on the central portion of the flange corresponding portions 62 and 63. In addition, the buckling limit stress is also reduced, and as a result, flange waves tend to be significantly generated.

[0104] In the case of single-pass rolling using the same pass, the pass shape that takes into account the flange stretching and the web stretching is designed based on the relationship with the shape of the previous pass, so that the flange wave can be suppressed. However, it is clear that in the case of two or more passes of rolling using the same pass, in the rolling after the second pass, the stretching of the web corresponding part, the flange corresponding part and the arm corresponding part is limited by the shape of the pass. Therefore, even if the shape of the pass is designed as in the past, the generation of flange waves in the middle of reversible rolling cannot be suppressed. According to the results of the study, the following is clarified: For example, in the case of reversible rolling, in the flange corresponding parts 62 and 63, at each rolling, the material is concentrated in the central part (near the neutral line) of these flange corresponding parts 62 and 63, which is easy to cause the phenomenon of flange thickness recovery. If the thickness recovery occurs, it will lead to an increase in the flange stretching in the next pass, and then it is easy to generate flange waves, which is not preferred.

[0105] In addition, if the first intermediate rolling mill 13 and the second intermediate rolling mill 16 are compared, the rolled piece (particularly the flange corresponding parts 62 and 63) is rolled thinner in the subsequent rolling mill, so the shape defect of the above-mentioned flange wave is likely to become significant. In addition, if shape defects occur in the process closer to the finishing rolling, it is likely to directly cause product shape defects. That is, from the perspective of product dimensional accuracy and rolling stability, it is important to solve the above-mentioned problems in the subsequent rolling mill.

[0106] In view of such problems, the inventors of the present application have conducted in-depth research on the shape of the pass set in the intermediate rolling mill, and as a result, have created a pass shape that satisfies the predetermined condition that the shape defect called flange wave mentioned above will not be generated. The detailed shape of the pass of the intermediate rolling mill that is configured to not generate flange wave will be described below with reference to the accompanying drawings. In addition, the rolling forming related to the flange corresponding portion 63 in the second intermediate rolling mill 16 is illustrated as an example, but the pass used as the object is a pass that reduces the thickness of the entire rolled piece, and is not limited to the pass of the second intermediate rolling mill 16.

[0107] Fig.16 1 is a schematic diagram illustrating an example of the structure of the pass 80 provided in the second intermediate rolling mill 16. Fig.16 (a) shows a schematic overall diagram. Fig.16 (b) shows the vicinity of the portion opposite to the flange corresponding portion 63 ( Fig.16 Here, Fig.16 (b) shows the state after rolling in the groove 80, and the rolled material after rolling is shown by a single-dot chain line.

[0108] like Fig.16 As shown, the pass 80 is composed of an upper pass roll 85 and a lower pass roll 88. The pass rolling in the pass 80 composed of the upper pass roll 85 and the lower pass roll 88 is used to reduce the thickness of the rolled piece as a whole (i.e., intermediate rolling). In addition, the rolling here is performed by, for example, reversible rolling in the same pass 80.

[0109] In addition, Fig.16In the pass 80 shown, the opposing portion 100 opposing the flange corresponding portion 63 of the rolled product includes a plurality of flange opposing portions 100a, 100b, 100c having different inclinations in order from the side close to the web. Regarding these flange opposing portions 100a, 100b, 100c, in this specification, there is a case where the flange opposing portion 100b is limited and referred to as the "first flange opposing portion", and the flange opposing portions 100a, 100c arranged on both sides of the first flange opposing portion are limited and referred to as the "second flange opposing portion" or the "third flange opposing portion". In addition, there is also a situation where the portion of the flange corresponding portion 6 that is formed by rolling the flange relative portion 100b located in the center is limited and called the "first flange portion", and the portions of the flange corresponding portion 6 arranged on both sides of the first flange portion (portions formed by rolling the flange relative portions 100a and 100c) are limited and called the "second flange portion" or the "third flange portion".

[0110] In addition, if Fig.16 As shown in (a) of FIG. 1 , the portion 101 facing the flange corresponding portion 62 of the rolled material is also composed of flange corresponding portions 101a, 101b, and 101c.

[0111] The inclination angles of the flange relative parts 100a, 100b, 100c relative to the horizontal line are θf2, θf1, θf3, respectively, and θf1 is an angle larger than θf2 and θf3. In addition, θf2 and θf3 may be equal angles. When the intervals tf2, tf1, tf3 (also called roller gaps) between the upper hole-shaped roller 85 and the lower hole-shaped roller 88 in the flange relative parts 100a, 100b, 100c are respectively constant (the flange relative parts 100a, 100b, 100c of the upper hole-shaped roller 85 and the lower hole-shaped roller 88 are parallel), the angles θf2, θf1, θf3 of the upper hole-shaped roller 85 and the lower hole-shaped roller 88 are equal. On the other hand, when the angles formed between the flange facing portions 100a, 100b, 100c and the horizontal line are different between the upper hole-shaped roll 85 and the lower hole-shaped roll 88, the angles θf2, θf1, θf3 may be set to the average value of the angles formed between the flange facing portions and the horizontal line of the upper hole-shaped roll 85 and the lower hole-shaped roll 88. In addition, these inclination angles θf2, θf1, θf3 are substantially the same even if they are defined by the angle formed between the center line S in the roll gap between the upper and lower hole-shaped rolls and the horizontal line.

[0112] The flange facing portion 100b is configured at a position straddling the neutral line O in the height direction, the flange facing portion 100a is located closer to the web side than the flange facing portion 100b, and the flange facing portion 100c is located closer to the arm (joint portion) side than the flange facing portion 100b. That is, the flange facing portion 100b is located at a position straddling the neutral line O, and the flange facing portions 100a and 100c are located on both sides of the flange facing portion 100b.

[0113] Here, the stretching of each pass is defined as the ratio of the thickness before rolling to the thickness after rolling (after one pass), the roll gap in the plate thickness direction in the hole 80 represents the thickness, and the roll gap reduction in the vertical direction of one pass in the reversible rolling process in the hole 80 is set to Δg. Then, the stretching λf1, λf2, and λf3 of the flange relative parts 100b, 100a, and 100c in each pass are expressed by the following equations (1) to (3).

[0114] λf1=tf'1 / tf1=(tf1+Δg·cosθf1) / tf1···(1)

[0115] λf2=tf'2 / tf2=(tf2+Δg·cosθf2) / tf2···(2)

[0116] λf3=tf'3 / tf3=(tf3+Δg·cosθf3) / tf3···(3)

[0117] In addition, tf'1, tf'2, and tf'3 are roll gaps corresponding to the thickness of the flange corresponding portion 63 before rolling corresponding to the flange corresponding portions 100b, 100a, and 100c in the pass 80, respectively. In addition, tf1, tf2, and tf3 are roll gaps corresponding to the thickness of the flange corresponding portion 63 after rolling by the flange corresponding portions 100b, 100a, and 100c in the pass 80, respectively.

[0118] That is, based on the relationship among tf1, tf2, and tf3, θf1 is set to an angle larger than θf2 and θf3, so that the following equations (4) and (5) are satisfied during rolling at the pass 80.

[0119] λf1<λf2···(4)

[0120] λf1<λf3···(5)

[0121] Here, the above equations (1) to (3) are used to express the stretching per single rolling pass. For the case where the stretching in the reversible rolling performed in multiple passes is summed up, the same correlation as equations (1) to (3) also holds. Therefore, in the pass 80, by setting θf1 to an angle larger than θf2 and θf3, the above equations (4) and (5) are satisfied not only for the stretching per pass, but also for the case where the stretching in multiple passes during the reversible rolling is summed up.

[0122] The rolled product that has been roll-formed in the pass 80 has a curved shape having multiple inclination angles in the flange corresponding parts 62 and 63. This shape is formed into a desired flat flange shape (flange shape of a hat-shaped steel sheet pile product) by using a pass that is later than the pass 80 set in the intermediate rolling mill, such as a pass set in the finishing mill 19 (finishing rolling process). In such flange flattening, reversible rolling is not performed. In addition, after the bending of the flange part is restored, stripe-like marks along the length direction are sometimes found at the boundary part of the bent part due to the difference in the adhesion state of the oxide scale between other parts, but such marks will not reduce the strength of the flange part, etc., and have no effect on the quality of the steel sheet pile.

[0123] According to the structure of such a pass 80, by increasing the angle θf1, the flange elongation near the neutral line O where compressive stress is likely to be generated is relatively reduced compared to the pass in which the flange opposing portion is linear (hereinafter also referred to as the conventional pass), and the flange elongation is relatively reduced compared to the flange elongation at a position away from the neutral line O, thereby achieving the effect of suppressing the generation of flange waves. On the other hand, by reducing the angles θf2 and θf3, the increase in the flange height is suppressed, and the elongation of the cross section of the flange corresponding portion 6 is maintained. For example, with respect to the angle θf1 determined as the flange wave suppression condition, in consideration of the suppression of the dimensional deviation when the desired flat flange shape is formed by rolling by the subsequent pass, the line length of the center line S of the pass 80 corresponding to the flange opposing portion (100a, 100b, 100c) is set to be the same as the line length of the center line of the flange opposing portion of the conventional pass, and the angles θf2 and θf3 may be designed in such a way that the horizontal position of the joint portion does not change. That is, if reversible rolling is performed in the pass 80, although the flange stretch is reduced in the flange opposing portion 100b compared with the conventional pass, the flange stretch is increased in the flange opposing portions 100a and 100c compared with the conventional pass, so that the flange as a whole can maintain the same flange cross-sectional stretch as that of the conventional pass. In addition, setting the line length of the center line S corresponding to the flange opposing portions (100a, 100b, 100c) of the pass 80 to be the same as the line length of the center line of the flange opposing portions of the conventional pass does not mean that they are completely the same, but means that they can be the same as long as they are within the range of error (for example, less than ±1% with respect to the line length of the center line of the flange opposing portions).

[0124] Here, in order to suppress the flange wave at the flange relative part 100b (hereinafter also referred to as the steeply inclined portion 100b) near the neutral line O, it is preferred to set the angle θf1 in such a way that the relationship between the stretch λf1 of the flange at the steeply inclined portion 100b and the stretch λw of the web corresponding portion 60 satisfies the following equation (6).

[0125] λf1≤λw···(6)

[0126] As a more detailed condition, it is desirable to set λf1 / λw per one pass to be within the range of 0.967≤λf1 / λw≤1.000.

[0127] The stretch of the flange is greatly affected by the stretch of the web, so the stretch of the flange corresponding part near the neutral line O is expressed in relation to the stretch of the web. In the case of a hat-shaped steel sheet pile, it is considered that the stretch of the arm corresponding parts 65 and 66 and the stretch of the web corresponding part 60 are substantially equal, so the stretch of the flange corresponding part near the neutral line O can be substantially expressed in relation to the stretch of the web. The stretch λw of the web in a single pass during the reversible rolling process is expressed by the following formula (7).

[0128] λw=tw' / tw=(tw+Δg·cosθw) / tw···(7)

[0129] Here, tw' is the roll gap corresponding to the thickness of the web corresponding portion 60 before rolling at the pass 80. In addition, tw is the roll gap corresponding to the thickness of the web corresponding portion 60 after rolling by the pass 80. In addition, θw is the inclination angle of the roll gap corresponding to the web corresponding portion 60 with respect to the horizontal line.

[0130] In the case of a hat-shaped steel sheet pile having a constant thickness in the flange width direction, in the pass 80 immediately before the finish rolling, the pass shape is designed so that the thicknesses of the flange facing portions 100a, 100b, and 100c are constant in the final pass except for errors due to roll wear, etc. However, since the inclination angle θf1 of the flange facing portion 100b is different from the inclination angles θf2 and θf3 of the flange facing portions 100a and 100c, the thicknesses are not constant in the middle passes of the pass 80. Therefore, the inclination angle and width of each flange facing portion may be determined based on the relationship between the thickness and the stretch of each flange facing portion and the stretch of the web corresponding portion, taking into account the stretch ratios λf1 / λw, λf2 / λw, and λf3 / λw in the pass where flange waves are most likely to be generated.

[0131] As described above, by increasing the inclination angle θf1 of the steeply inclined portion 100 b , it is possible to reduce the flange elongation near the neutral line O and reduce the compressive stress generated in this portion.

[0132] As mentioned above Fig.16 As described above, the pass shape of the pass 80 for intermediate rolling is set to a shape having a plurality of flange-opposing portions 100a, 100b, 100c with different inclination angles, and the inclination angles of these flange-opposing portions 100a, 100b, 100c are set to the preferred conditions shown in the above equations (1) to (6), so that the compressive stress generated near the neutral line O of the flange corresponding portion 63 can be reduced during the rolling forming using the pass 80, and the generation of flange waves can be suppressed. In addition, the recovery of the flange thickness generated by the concentration of materials near the neutral line of the flange corresponding portion 63 during the reversible rolling can be reduced, thereby further suppressing the generation of flange waves.

[0133] On the other hand, compared with the flange stretch generated near the neutral line O (i.e., the flange stretch at the flange corresponding part 100b), the flange stretch generated at the flange corresponding parts 100a and 100c is relatively increased, and the compressive stress generated there is also increased, but in addition to separation from the neutral line O, the compressive stress does not become too large because the metal flow to the web corresponding part 60 and the arm corresponding part 66 is easy to occur. In addition, in the flange corresponding part 63, the parts corresponding to the flange corresponding parts 100a and 100c are connected to the web corresponding part 60 and the arm corresponding part 66, and buckling is not likely to occur. From this point of view, flange waves are not likely to occur in these parts.

[0134] In this way, by setting the hole shape of the hole 80 to have a plurality of flange corresponding parts 100a, 100b, 100c with different inclination angles, it is possible to suppress the flange waves generated near the neutral line O of the flange corresponding parts 62, 63 of the rolled piece compared to the rolling forming using the conventional hole shape, thereby achieving improved product dimensional accuracy and rolling stability. Depending on the product shape, in rolling using the conventional hole shape, sometimes the stretching of the flange corresponding parts 62, 63 is greater than the stretching of the web corresponding part 60, and it is impossible to maintain balance and suppress the flange waves. In this case, instead of changing the inclination angle of the entire flange, as shown in FIG. Fig.16 As shown, the inclination angle θf1 of the steeply inclined portion 100b is made larger than the flange inclination angle of the previous hole shape and larger than the inclination angle of the flange relative parts 100a and 100c, thereby suppressing the increase in the height of the rolled piece during rolling forming and effectively suppressing the flange wave.

[0135] (Other shapes of holes used in intermediate rolling)

[0136] In addition, the hole-shaped portion relative to the flange corresponding portions 62, 63 of the rolled workpiece (i.e., the flange relative portion 100) may be, relative to the straight line connecting the boundary portion on the arm side (of the rolled workpiece) and the boundary portion on the web side (of the rolled workpiece), wherein at a position closer to the arm side of the flange relative portion near the neutral line O, the hole-shaped portion is a convex shape protruding toward the inner side of the flange, and at a position closer to the web side of the flange relative portion near the neutral line O, the hole-shaped portion is a convex shape protruding toward the outer side of the flange.

[0137] Specifically, regarding the shape of the flange facing portion 100 provided with the steeply inclined portion 100b, it is not necessary to form the shape of each flange facing portion 100a to 100c in a straight line shape. As long as the inclination angles of the flange facing portions 100a, 100b, and 100c are the preferred conditions shown in the above equations (4) to (6), for example, a part or all of each flange facing portion 100a to 100c may be formed by a curve. In this case, the steeply inclined portion 100b is defined as a range sandwiched by the intersection point with the flange facing portion 100a and the intersection point with the flange facing portion 100c, and the steeply inclined portion 100b is formed so as to straddle the neutral line O.

[0138] Fig.17 2 is a schematic diagram of another shape of the hole used in the intermediate rolling, and is a schematic enlarged diagram showing an example of the vicinity of the portion corresponding to the flange corresponding portion 63. Fig.17 As shown, the flange corresponding parts 100a, 100c are composed of a curved shape. Preferably, the process of performing reversible rolling includes the process of forming a web corresponding part 60 and an arm corresponding part 66, wherein the web corresponding part 60 is connected to a flange part (also referred to as a web side flange part) including at least one second flange part, and the arm corresponding part 66 is connected to a flange part (also referred to as an arm side flange part) including at least one third flange part. In this case, it is preferred to include a web corresponding part 100d for forming the web corresponding part 60 and an arm corresponding part 100e for forming the arm corresponding part 66. Here, the pass preferably includes a web side flange corresponding part group including at least one flange corresponding part 100a (second flange corresponding part) and an arm side flange corresponding part group including at least one flange corresponding part 100c (third flange corresponding part). Here, the boundary between the web-side flange facing portion group and the web facing portion 100d is represented by Pa, and the boundary between the arm-side flange facing portion group and the arm facing portion 100e is represented by Pc.

[0139] exist Fig.17In the example shown, with respect to the straight line Q connecting the boundary Pc on the arm side (the boundary between the arm corresponding part 100e and the flange corresponding part 100c corresponding to the arm corresponding part 66) and the boundary Pa on the web side (the boundary between the web corresponding part 100d and the flange corresponding part 100a corresponding to the web corresponding part 60), the flange corresponding part 100a is a curved shape of a convex shape protruding toward the outer side of the flange, and the flange corresponding part 100c is a curved shape of a convex shape protruding toward the inner side of the flange. In addition, in this modified example, the steeply inclined part 100b is shown as a straight line shape, but the steeply inclined part 100b may also be set to a curved shape.

[0140] In such Fig.17 When the flange facing parts 100a and 100c shown in the figure are in a curved shape, the inclination angles θf2 and θf3 of the flange facing parts 100a and 100c are determined by the tangent lines ( Fig.17 The inclination angle of Qa, Qc) relative to the horizontal line can be determined. When the steeply inclined portion 100b is a curved shape, the inclination angle can be determined based on the tangent line with the largest angle. Fig.17 In the figure, the straight line Q and the tangent lines Qa and Qc are described with reference to the lower hole roll 88, but they can be determined similarly for the upper hole roll 85. Furthermore, when the angles formed between the flange opposing parts 100a, 100b, 100c and the horizontal line are different between the upper hole roll 85 and the lower hole roll 88, θf2, θf1, and θf3 can be set to the average value of the angles formed between the flange opposing parts of the upper hole roll 85 and the lower hole roll 88 and the horizontal line. The same effect can be obtained by setting the inclination angles of the flange opposing parts 100a to 100c defined in this way to the preferred conditions shown in the above equations (1) to (6).

[0141] That is, the hole shape of the hole 80 is described here as a shape having a plurality of flange corresponding parts 100a, 100b, 100c with different inclination angles, and the detailed shape of each part 100a, 100b, 100c is not mentioned. The shape of the flange corresponding parts 62, 63 can be composed of a plurality of straight lines or curves, or a combination of the two, and the shape of each part 100a, 100b, 100c can be arbitrarily designed accordingly. In the case where the flange corresponding parts 62, 63 are assumed to constitute a curved part, the inclination angle of the curved part can be defined by the angle of its tangent.

[0142] (Individual production of different sizes with different thicknesses)

[0143] The rolling line L described in the above embodiment is preferably configured to cope with the case of manufacturing products of different thicknesses. In the bending machine 20 of the rolling line L, it is also preferred not to perform plate thickness reduction of the finished workpiece 19a as in the above embodiment. That is, after the thickness of the finished workpiece 19a is made the thickness dimension of the product by the rolling process (rough rolling to finishing rolling), the finished workpiece 19a is formed into a cross-sectional shape similar to the cross-sectional shape of the product by the bending machine 20 without performing plate thickness reduction on the finished workpiece 19a. In this case, in the bending machine 20, the roll gaps in the pass 45 and the pass 55 are adjusted to cope with the thickness changes of the web corresponding portion 60 and the flange corresponding portions 62, 63 of the finished workpiece 19a.

[0144] Here, for example Fig.18 As shown in FIG. 1 , in the pass 45, the roll gap of the portion 45a (hereinafter referred to as the web portion 45a) corresponding to the web corresponding portion 60 is set to tw, the roll gap of the portion 45b (hereinafter referred to as the flange portion 45b) corresponding to the flange corresponding portions 62 and 63 is set to tf, and the angle of the flange portion 45b relative to the web portion 45a (hereinafter referred to as the flange angle) is set to θ. In addition, if the roll gap of the pass 45 is increased by Δ in the vertical direction, as shown in FIG. Fig.18 As shown by the dotted line, the roll gap of the web portion 45a increases by Δtw (=Δ), and the roll gap of the flange portion 45b increases by Δtf (=Δcоsθ).

[0145] The flange angle of the pass in the rolling mill (roughing mill 10 to finishing mill 19) of the rolling process is different from the flange angle θ in the bending machine 20. Therefore, even if the roll gaps of the rolling mill and the bending machine 20 are adjusted by the same amount, the change amount Δtf of the flange portion 45b in these rolling mills and the bending machine 20 is different. Specifically, the flange angle θ in the bending machine 20 is larger than the flange angle of the finishing mill 19, so the change amount Δtf in the bending machine 20 is smaller than the change amount Δtf in the finishing mill 19. As a result, the plate thickness of the finished product 19a may be reduced at the flange portion 45b in the bending machine 20. Therefore, it is necessary to set the roll gap change amount in the rolling mill and the roll gap change amount in the bending machine 20 separately according to the thickness change of the product.

[0146] That is, the amount of change in the roll gap in the rolling mill is set so that the thickness of the finished workpiece 19a becomes the thickness dimension of the product.

[0147] On the other hand, the roll gap variation in the bending machine 20 is set so that the thickness of the finished product 19a is not reduced for all the assumed thicknesses when the finished product 19a is formed by the bending machine 20. In other words, the roll gap in the bending machine 20 is set to be larger than the assumed total thicknesses in accordance with the thickness variation of the finished product 19a. Specifically, when the roll gap of the reference part in the bending machine 20, for example, the web part 45a of the pass 45, is set to be larger by A than the thickness of the product at the part so that the thickness of the finished product 19a is not reduced at the web part 45a (product thickness + A), the roll gap of the flange part 45b is set to be larger by B than the thickness of the product at the part (product thickness + B) so that the thickness of the finished product 19a is not reduced in the flange part 45b either. These A and B are respectively larger than 0, preferably 5 mm or less, and more preferably 0.5 mm to 3 mm. In addition, the upper grooved roll 40 and the lower grooved roll 41 forming the groove 45 are designed so that the above-mentioned roll gap can be set.

[0148] In the above description, the roll gap of the flange portion 45b is set to the thickness of the product + B, and the roll gap of the arm portion of the hole 45 that is opposite to the arm corresponding portion 65, 66 is also set to the thickness of the product + C. C is also larger than 0, as is A and B, and is preferably 5 mm or less, and more preferably 0.5 mm to 3 mm. In the case of a hat-shaped steel sheet pile, the web corresponding portion and the arm corresponding portion of the product are horizontal, so A and C are approximately the same. In addition, the roll gap of the other hole 55 is also set in the same way as the roll gap of the above-mentioned hole 45.

[0149] According to this mode, the same effects as those of the above-mentioned embodiment are achieved, and products of different thicknesses can be manufactured by adjusting the roll gap using the same upper and lower grooved rolls of the bending machine 20. Therefore, the degree of freedom in the size of the product that can be manufactured can be increased.

[0150] (other)

[0151] For example, in the above-mentioned embodiment, the bending machine 20 is illustrated as being composed of the first frame 22 and the second frame 23, but the present invention is not limited thereto. For example, the bending machine 20 may be a single frame, or may be composed of any number of multiple frames. In the case where the bending machine 20 is composed of multiple frames, the bending can be performed in a shared manner in each frame, so that the shape change of the corresponding parts 68 and 69 of the joint portion caused by the bending can be reduced. In addition, the number of frames is appropriately determined based on the balance between the bending angle and the equipment investment. For example, if the bending angle is about 20° to 30°, two frames are preferred.

[0152] In the bending machine 20 described in the above embodiment, it is preferable to supply lubricating oil or the like to the contact portion between the rolled workpiece (finished workpiece 19a) and each grooved roller for lubrication. In particular, the lower surface of the web corresponding part 60 and the upper surface of the arm corresponding parts 65 and 66 are partially in contact with the grooved roller, and the relative sliding speed is relatively large. Therefore, scratches are easily generated in this area of ​​the product after bending. Therefore, in particular, the contact portion between the lower surface of the web corresponding part 60 and the upper surface of the arm corresponding parts 65 and 66 and the grooved roller needs to be lubricated. By performing such lubrication, a product with good quality and no scratches can be manufactured.

[0153] In addition, although the above embodiments and their modified examples illustrate the case where a hat-shaped steel sheet pile product is manufactured in an upward open position (where the arm corresponding part is located on the upper side relative to the web corresponding part), the present invention can also be applied to the case where the product is manufactured in an opposite downward open position (where the arm corresponding part is located on the lower side relative to the web corresponding part). In this case, it is considered that the direction of the joint portion and the upper and lower hole-shaped rollers can be arranged oppositely. In addition, although the case of manufacturing a hat-shaped steel sheet pile as a final product is cited as an example in the description of the above embodiments and their modified examples, the present invention is not limited to this and can also be applied to the manufacture of steel sheet pile products such as U-shaped steel sheet piles.

[0154] Example

[0155] (Example 1)

[0156] The following cases were compared: a case where a hat-shaped steel sheet pile was manufactured by using the manufacturing method of the steel sheet pile of the present invention, followed by hot finish rolling and hot bending at 20° using a bending forming machine composed of two continuous frames; and a case where a hat-shaped steel sheet pile was manufactured by using a plurality of supporting rollers composed of flat rollers and bending by cold working as the prior art.

[0157] According to the manufacturing method of the steel sheet pile of the present invention, after the rolled piece after bending is cut into product length, the angle between the flange and the web increases by about 0.5° at most due to springback. In addition, the overall width difference in the product length direction at this time is about 4.5 mm.

[0158] On the other hand, according to the conventional method for manufacturing steel sheet piles, after the rolled piece after bending is cut into product length, the angle between the flange and the web increases by about 2.2° at most due to springback. In addition, the overall width difference in the product length direction at this time is about 25 mm.

[0159] (Example 2)

[0160] As Example 2 of the present invention, the first hat-shaped steel sheet pile product (steel sheet pile 1 in the table) having a web thickness of 15.0 mm, a flange thickness of 11.3 mm, and an arm thickness of 14.5 mm and the second hat-shaped steel sheet pile product (steel sheet pile 2 in the table) having a web thickness of 17.0 mm, a flange thickness of 12.8 mm, and an arm thickness of 16.5 mm are manufactured using the same bending forming rollers. Therefore, the rollers of the finishing mill and the bending forming machine of the two stands are respectively shared under the dimensional conditions shown in the following Table 1, and only the roll gap is adjusted to perform hot bending and forming for manufacturing.

[0161] [Table 1]

[0162]

[0163] As shown in Table 1, the bending forming was performed with the roll gap of either the first stand or the second stand of the bending forming machine being 1.9 mm to 2.8 mm larger than the thickness of the finished workpiece (i.e., the roll gap of the finishing mill). This enables the manufacture of good products by adjusting the forming roll gap at a very low forming load compared to the finishing rolling.

[0164] (Example 3)

[0165] As Example 3 of the present invention, the difference in finishing temperature of the rolled piece after intermediate rolling between the intermediate rolling method using two pass types in the prior art and the intermediate rolling method using a single pass type and multiple passes in the present invention was verified. The following Table 2 is a table showing the rolling conditions in the intermediate rolling of the prior art method and the method of the present invention. In addition, Fig.19 is an explanatory diagram related to the present embodiment 3, Fig.19 (a) represents the hole configuration of the existing method, Fig.19 (b) shows the hole configuration of the method of the present invention.

[0166] [Table 2]

[0167] Existing methods The present invention Number of holes (intermediate forming) Two hole types Single hole type Number of passes (intermediate shaping) Four passes Four passes Flange finishing temperature 680℃ 720℃

[0168] like Fig.19 As shown in (a) and Table 2, in the conventional method, two pass types are arranged in parallel, and each pass type is rolled two times. Fig.19 (b) As shown in Table 2, in the method of the present invention, the single-pass type is arranged in series and multiple passes are rolled. As a result, it is found that as shown in Table 2, the conventional method takes time to translate the steel material, while the method of the present invention does not require translation of the steel material, so the flange finishing temperature is 40°C higher.

[0169] In addition, when the present invention is applied, the roller body length is shortened, so there is an effect of improving the roller load resistance. In the production of hat-shaped steel sheet piles, especially for thin-walled sizes and sizes with a large number of passes, the amount of reduction per pass can be increased, so a large pass number reduction effect can be expected. In this case, the flange finishing temperature can be greatly increased to more than the flange finishing temperature shown in Table 2.

[0170] If the finishing temperature of the steel material (rolled material) during the intermediate rolling is high, there is an advantage that the steel material can be sawed efficiently with less processing energy. In addition, when the bending forming described in the above embodiment is performed, the forming load applied to the bending forming machine, the elongation and toughness reduction caused by the bending forming, and the material degradation and residual stress can be reduced.

[0171] Industrial Applicability

[0172] The present invention can be applied to a method for manufacturing a hat-shaped steel sheet pile.

[0173] Description of Reference Numerals

[0174] 10. Roughing mill; 13. First intermediate mill; 14. Edger; 16. Second intermediate mill; 17. Edger; 19. Finishing mill; 19a. Finished workpiece; 20. Bending machine; 22. First stand; 23. Second stand; 40. Upper hole-shaped roller; 41. Lower hole-shaped roller; 44. Shell; 45. Pass; 50. Upper hole-shaped roller; 51. Lower hole-shaped roller; 54. Shell; 55. Pass; 60. Web corresponding part; 62, 63. Flange corresponding part; 65, 66, arm corresponding parts; 68, 69, joint corresponding parts; 70, corner; 70a, 70b, inside of corner; 70c, 70d, outside of corner; 71, corner; 71a, 71b, inside of corner; 71c, 71d, outside of corner; 80, hole type (for intermediate rolling); 100, opposite part; 100a~100c, flange opposite part; 101a~101c, flange opposite part; L, rolling production line; O, neutral line.

Claims

1. A method for manufacturing a hat-shaped steel sheet pile, wherein a rolled piece is subjected to rough rolling, intermediate rolling and finish rolling by hot rolling and then bent and formed. It is characterized in that The rolled piece includes a web corresponding portion, a flange corresponding portion, an arm corresponding portion and a joint corresponding portion. A corner portion as a processing portion is formed at a connection portion between the web corresponding portion and the flange corresponding portion and a connection portion between the flange corresponding portion and the arm corresponding portion. In one or more intermediate rolling mills consisting of a single stand and a single groove, the intermediate rolling is performed on the hot rolled product in multiple passes at a height lower than a predetermined target product height using the grooves provided on the upper and lower grooved rolls. The bending is performed in a hot state and at a temperature of the processed portion that is higher than the phase transformation point, so that the rolled piece is formed into a predetermined target height and a target width.

2. The method for manufacturing a hat-shaped steel sheet pile according to claim 1, It is characterized in that The intermediate rolling includes a step of reversibly rolling the rolled piece using the same pass. The reversible rolling step includes forming a first flange portion straddling a neutral line and a second flange portion and a third flange portion disposed on both sides of the first flange portion. The groove for performing the reversible rolling comprises a first flange facing portion for forming the first flange portion, a second flange facing portion for forming the second flange portion, and a third flange facing portion for forming the third flange portion. The inclination angle of the first flange facing portion with respect to the horizontal plane is larger than the inclination angles of the second flange facing portion and the third flange facing portion with respect to the horizontal plane.

3. The method for manufacturing a hat-shaped steel sheet pile according to claim 2, It is characterized in that The step of performing reversible rolling includes the step of forming the web corresponding portion and the arm corresponding portion. The pass for performing the reversible rolling comprises a web-opposing portion for forming the web-opposing portion and an arm-opposing portion for forming the arm-opposing portion, The groove for performing the reversible rolling comprises: a web side flange relative portion group including at least one of the second flange relative portions; and an arm side flange relative portion group including at least one of the third flange relative portions. With respect to a straight line connecting a boundary between the web-side flange opposing portion group and the web-side opposing portion and a boundary between the arm-side flange opposing portion group and the arm-side opposing portion, The second flange-facing portion is convex and protrudes toward the outer side of the flange. The third flange facing portion is in a convex shape that bulges toward the inner side of the flange.

4. The method for manufacturing a hat-shaped steel sheet pile according to claim 2 or 3, It is characterized in that In the groove for performing the reversible rolling, rolling is performed so that the flange elongation (λf1) at the first flange portion is smaller than the flange elongation (λf2) at the second flange portion and the flange elongation (λf3) at the third flange portion.

5. The method for producing a hat-shaped steel sheet pile according to any one of claims 1 to 3, It is characterized in that The bending is performed using upper and lower hole-shaped rollers. In the bending forming, the upper and lower grooved rollers are used so that parts of the upper and lower grooved rollers come into contact with the inner side of the corner portion, thereby bending the corner portion.

6. The method for producing a hat-shaped steel sheet pile according to any one of claims 1 to 3, It is characterized in that In the bending forming, the roller is brought into contact with the corner portion in a direction balanced with the force applied as the roller contacts the other corner portion which is the connection portion between the web corresponding portion and the flange corresponding portion, thereby applying force to the other corner portion which is the connection portion between the flange corresponding portion and the arm corresponding portion.

7. The method for producing a hat-shaped steel sheet pile according to any one of claims 1 to 3, It is characterized in that The bending is performed using upper and lower hole-shaped rollers. In the bending forming, the upper and lower grooved rollers are used in a hot state so that parts of the upper and lower grooved rollers are brought into contact with the inner side of the corner portion, thereby bending the corner portion. During the bending forming, the roll gap of the upper and lower hole-shaped rollers corresponding to the web corresponding part, the flange corresponding part and the arm corresponding part is larger than the thickness of the web corresponding part, the flange corresponding part and the arm corresponding part.

8. The method for manufacturing a hat-shaped steel sheet pile according to claim 7, It is characterized in that In accordance with changes in thickness of the web corresponding portion and the flange corresponding portion, the roll gaps of the upper and lower grooved rolls performing the bending forming at portions facing the web corresponding portion and the flange corresponding portion are set larger than the respective thicknesses.

9. The method for manufacturing a hat-shaped steel sheet pile according to claim 7, It is characterized in that In the hot rolling, the rolled piece is rolled so that the thickness of the corner portion is greater than the product thickness. In the bending forming, the corner portion is pressed down by the upper and lower grooved rollers.

10. The method for manufacturing a hat-shaped steel sheet pile according to claim 7, It is characterized in that During the bending process, the contact portion between the rolled workpiece and the upper and lower grooved rollers is lubricated.

11. The method for manufacturing a hat-shaped steel sheet pile according to claim 7, It is characterized in that In the bending forming, the upper and lower grooved rollers are brought into contact with the outer side of the web corresponding portion and the outer surface of the arm corresponding portion.

12. The method for manufacturing a hat-shaped steel sheet pile according to claim 7, It is characterized in that In the bending forming, the upper and lower grooved rollers are brought into contact with the outer surface of the joining portion corresponding portion so that the joining portion corresponding portion becomes substantially horizontal.

13. The method for producing a hat-shaped steel sheet pile according to any one of claims 1 to 3, It is characterized in that The bending machine for performing the bending and the finishing mill for performing the finishing rolling are connected in series.

14. The method for producing a hat-shaped steel sheet pile according to any one of claims 1 to 3, It is characterized in that The processed parts are connection parts between the web corresponding part and the flange corresponding part and connection parts between the flange corresponding part and the arm corresponding part, and are curved parts having a curvature.

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